Particles suitable for use in electrophoretic displays (EPD), e.g. coloured electronic paper have been exemplified in recent patent literature; e.g. (U.S. Pat. No. 7,304,634, GB 2 438 436, US 2007/0268244). It is now possible to control and manipulate features such as size, colour, charge and polydispersity independently to produce particles with desired properties for EPD; e.g. WO 2010089057. A number of different techniques can be used to create an optical effect by the movement of particles. One such method could incorporate the use of reflective colour particles, and absorbing black particles to generate a pixel that can be switched between a colour, and a black optical state.
The biggest challenge of such a system is obtaining a highly reflective colour state. Typical colour pigments that can be dispersed in solvents used for EPD do not show a high enough reflectivity to generate an appropriate optical difference. In addition, colour tuning of pigments is restrictive and the choice of colours is limited. High resolution Printing and dispensing of such pigment dispersions is also very challenging. So, there continues to be a demand for improved electrophoretic fluids.